Important!

There are a lot of existing Jenkins plugins, and a lot of people with Jenkins plugin development experience that you can take advantage of!

Check whether there is an existing plugin you can already use, or contribute to, then get in touch via the jenkinsci-dev mailing list, or IRC and explain your plugin idea.
Either we can point you towards an existing plugin, useful APIs, or code snippets that would be helpful.

Table of Contents

What Can Plugins Do?

Jenkins defines extensibility points, which are interfaces or abstract classes that model an aspect of a build system. Those interfaces define contracts of what need to be implemented, and Jenkins allows plugins to contribute those implementations. See this document for more about extension points.

In this document, we'll be implementing a Builder that says hello. (built-in builders include Ant, Maven, and shell script. Builders build a project.)

Setting Up Environment

If you are using the Nexus Maven Repository Manager, you can ignore these instructions, and instead, click here for instructions on how to add Jenkins build prerequisites and the proper settings.xml entries.

It may be helpful to add the following to your ~/.m2/settings.xml (Windows users will find them in %USERPROFILE%\.m2\settings.xml):

This will let you use short names for Jenkins Maven plugins (i.e. hpi:create instead of org.jenkins-ci.tools:maven-hpi-plugin:1.61:create),
though this is unnecessary once you are already working in a plugin project (only useful for initial hpi:create).
Note that adding the Jenkins repositories in a profile like this is not really necessary since most (all?) plugins already define these repositories.
And the mirror declaration is probably unnecessary.

Creating a New Plugin

To start a new plugin, use an IDE (below), or if you are more comfortable with Maven, run the following command:

This will ask you a few questions, like the groupId (the Maven jargon for the package name) and the artifactId (the Maven jargon for your project name), then create a skeleton plugin from which you can start with. Make sure you can build this:

$ cd newly-created-directory
$ mvn package

Explanations:

-U means that Maven should update all relevant Maven plugins (check for plugin updates)hpi: this prefix specifies that the Jenkins HPI Plugin is being invoked, a plugin that supports development of Jenkins pluginscreate is the goal which creates the directory layout and the POM for your new Jenkins plugin and it adds it to the module listpackage is a standard phase which compiles all sources, runs the tests and creates a package - when used by the HPI plugin it will create an *.hpi file

Building a Plugin

To build a plugin, run mvn install. This will create the file ./target/pluginname.hpi that you can deploy to Jenkins.

$ mvn install

Setting up a productive environment with your IDE

NetBeans

NetBeans users can use the IDE's Maven support to open the project directly.

As you navigate through the code, you can tell NetBeans to attach source code JAR files by clicking the "Attach" button that appears in the top of the main content window. This allows you to read the Jenkins core source code as you develop plugins. (Or just select Download Sources on the Dependencies node.)

IntelliJ IDEA

IntelliJ 7.0 (or later) users can load pom.xml directly from IDE, and you should see all the source code of libraries and Jenkins core all the way to the bottom. Consider installing IntelliJ IDEA plugin for Stapler to make the development easier.

IntelliJ defaults to downloading sources and JavaDocs on demand. So, to see the source, you may need to click the Download artifacts button in the Maven Projects tab.

Eclipse

Use Eclipse Juno (4.2) or later for the best experience.

As Jenkins plugins are Maven projects, Eclipse users have two ways to load a Jenkins plugin project. One is to use m2e, which tries to make Eclipse understand Maven "natively", and the other is to use Maven Eclipse plugin, which makes Maven generate Eclipse project definitions. At the moment, unless you have some prior experience with m2e, we currently recommend plugin developers to go with the Maven Eclipse plugin.

Eclipse users can run the following Maven command to generate Eclipse project files (the custom outputDirectory parameter is used to work around the lack of JSR-269 annotation processor support in Eclipse:)

If the project is created using the provided archetype, everything is already set up. Up to Jenkins 1.645 the Plugin Parent POM was part of the main Jenkins project and the POM version was the baseline Jenkins version to be used for the plugin.

When using Parent POM version 2.2 or later, the baseline version is selection using the jenkins.version property, e.g.:

<properties>
<jenkins.version>1.609.1</jenkins.version>
</properties>

src/main/java

Java source files of the plugin.

src/main/resources

Jelly/Groovy views of the plugin. See this document for more about it.

src/main/webapp

Static resources of the plugin, such as images and HTML files.

Source Code

PluginImpl approach

(deprecated in favor of the Extension points approach below)

A plugin's main entry point may be a PluginImpl class that extends from Plugin. Once Jenkins detects this plugin class (via its inheritance relationship from Plugin), it will create an instance, and invoke methods.

Extension points approach

A Plugin class is optional; a plugin may simply implement extension points, registering them with the @hudson.Extension annotation for automatic detection by Jenkins.

The bulk work in the plugin consists in implementing those extension points. See the sample source code for more information about how a Builder is implemented and what it does.

Here are a few things about extension:

in general a plugin extension should extend an existing extension point (a class that implements ExtensionPoint), and define an inner static class extending the corresponding descriptor (a class extending hudson.model.Descriptor)

the @Extension annotation must be placed on the inner descriptor class to let Jenkins know about this extension

the descriptor handles the global configuration of the extension while the extension class itself handles the individual configuration of the extension. For instance in a plugin defining a class extending LabelAtomProperty, an object of this class is instantiated for each LabelAtom (provided that the plugin is activated by the user in the label's configuration page). If configuration parameters for each individual instance are required, they're handled via a config.jelly file stored in a resource package named after the extension class. When the configuration form is saved, Jenkins calls the extension constructor marked with the @org.kohsuke.stapler.DataBoundConstructor annotation, matching parameters by name

Debugging a Plugin

NetBeans 6.7+ users can just hit Debug. For all others, run the following command to launch Jenkins with your plugin:
Convenient:

If you open http://localhost:8080/jenkins in your browser, you should see the Jenkins page running in Jetty. The MAVEN_OPTS portion launches this whole thing with the debugger port 8000, so you should be able to start a debug session to this port from your IDE.

Once this starts running, keep it running. Jetty will pick up all the changes automatically.

When you make changes to view files in src/main/resources or resource files in src/main/webapp, just hit F5 in your browser to see the changes.

When you change Java source files, compile them in your IDE (NetBeans 6.7+: Debug > Apply Code Changes) and Jetty should automatically redeploy Jenkins to pick up those changes. There is no need to run mvn at all.

MAVEN_OPTS can be used to specify all sorts of other JVM parameters, like -Xmx

Changing port

If you need to launch the Jenkins on a different port than 8080, set the port through the system property jetty.port.

$ mvn hpi:run -Djetty.port=8090

Setting context path

maven-hpi-plugin 1.65 or later (used by parent POM 1.401 or later) can set the context path by using a system property. On more recent versions of Jenkins the "/jenkins" prefix is added automatically.

$ mvn hpi:run -Dhpi.prefix=/jenkins

Changing code while debugging

Depending on what you change, you can see it in the running instance without restarting the whole Maven process:

Views: Groovy/Jelly views are re-compiled every time a browser requests a page, so just reload a page in the browser and you'll see the changes. This is also true for help files you write.

Java code: If you are debugging, JVM's hot swap feature can be used to reload code so long as you do not touch the method signature. (For example, from NetBeans use Debug » Apply Code Changes.) Beyond that, you can hit ENTER in the Maven process and it'll reload the Jenkins webapp, though generally it is better to stop the process and start again. See Developing with JRebel for how to get a JRebel license for OSS projects to improve this experience.

POM: If you change POM, you'll have to stop and restart Maven to see the changes.

If you are using version 1.120 or later of maven-hpi-plugin, which would be the default when using version 2.16 or later of the plugin parent POM, you can use the same features to debug changes spanning multiple plugins, or even a custom build of Jenkins core. Just make sure you have SNAPSHOT dependencies set up between the associated Maven modules (<scope>test</scope> suffices), and that the upstream module(s) have been built (e.g., mvn -DskipTests clean install). Now hpi:run on the downstream plugin and you should be able to reload views defined in any of the linked modules.

Distributing a Plugin

To create a distribution image of your plugin, run the following Maven command:

$ mvn package

This should create target/*.hpi file. Other users can use Jenkins' web UI to upload this plugin to Jenkins (or place it in $JENKINS_HOME/plugins.)

Releasing a Plugin and Hosting a Plugin on jenkins-ci.org

If you got to this point, you should definitely consider hosting your plugin on jenkins-ci.org. Move on to this document for how to do that. This includes the instructions for releasing the plugin.

Using custom builds of plugins included in the Jenkins WAR

If you are building a patched version of one of the plugins in the Jenkins core, the deployment process is a bit different. This is because Jenkins will itself manage these plugins unless you tell it not to.

Other tips

Consider running Maven like this mvn -o ... to avoid hitting repositories every time. This will make various operations considerably faster.

Subscribe to the users' alias from here so that we can get in touch with you.

When you bump up the version of Jenkins you depend on, make sure to run mvn clean once, in particular to delete target/work that Jetty uses. Newer versions may just use work, not target/work. Otherwise your Jetty may continue to pick up old left-over JAR files.

If you have a high latency network connection to the Maven repository, you might find it faster to first run the build once on a server near to the maven repository, then rsync the .m2/repository folder across to your local computer

The 'package' and 'install' targets will by default run many tests. You can add '-DskipTests' on the command-line to skip these (of course you should run the tests before committing any changes)

The 'compiler:compile' goal is faster than 'compile', because it is a goal, rather than a lifecycle event, and therefore avoids certain earlier goals, such as setting up resources

Other resources

Besides this tutorial, there are other tutorials and examples available on line: